Sarah, Sherlock now understood, had been biding her time. Whether or not she had been specifically thinking ahead to Christmas - it was possible, she was no fool - her willingness to retain John at the surgery, which had initially registered as convenient if inexplicable forbearance, Sherlock now understood to be in service of a darker purpose.
John arrived home two hours later than usual, irritable and sticky with pine sap.
"Waiting room Christmas tree," John said, by way of extraneous explanation. "I do owe her," he added pointedly.
Sherlock ignored this. "Tea?" he asked.
"Need a wash first, thanks," John muttered.